The Second Latin American School in Mathematics was held during the month of July at the Centro de Investigacion
del IPN, in Mexico City and was dedicated to the memory of
Heinz Hopf. The School was held under the auspices of the
Centro de Investigacion del IPN, Organization of American
States, The National Science Foundation and the Consejo
Nacional de Ciencia y Tecnologia.
These notes contain three of the seven series of
lectures given at the School. We hope that the others will
appear at some future date. We thank the participants and
the lecturers for having made the School a most stimulating
mathematical event.